Lubricant compositions are generally well known in the art and are broadly categorized as oil or water based compositions, i.e., compositions that include large weight percentages of non-polar compounds (such as (base) oils) or large weight percentages of water, respectively. Lubricant compositions are typically further categorized as engine oils, driveline system oils, gear oils, greases, automatic and manual transmission fluids and oils, hydraulic oils, industrial gear oils, turbine oils, rust and oxidation (R&O) inhibited oils, compressor oils, or paper machine oils, etc. Each of these compositions has particular specifications and design requirements and most are designed to minimize corrosion and wear, to resist thermal and physical breakdown, and to be able to minimize the effects of common contaminants such as oxidizing compounds and metal fragments.
Antioxidants are compounds that can retard oxidation, and thus are useful as additives in such lubricant compositions. Antioxidants are commonly utilized in lubricant compositions to assist in reducing unwanted oxidation and increasing performance standards. Combustion engine lubricants oxidize readily at the high operating temperatures of an engine, and in turn, have diminished lubricating capacity as the viscosity of the lubricant increases. Oxidation products also tend to accumulate to form deposits, which in turn leads to greater wear on engine parts. For example, peroxyl radicals can lead to formation of radical chains and ultimately oxidative degradation. Antioxidants are used to react with such radicals, shorten radical chains, and reduce degradation. Unfortunately, many antioxidants do not react as fast as would be desired. Therefore, remains an opportunity for development of improved antioxidants.